This is NOT a duplicate. The other answers do not apply to this situation.
When trying to boot a 64 bit image in a headless VirtualBox, I get
This kernel requires an x86-64 CPU, but only detected an i686 CPU. Unable to boot – please use a kernel appropriate for your CPU
My processor is 64 bit.
Linux medusa 3.13.0-32-generic #57-Ubuntu SMP Tue Jul 15 03:51:08 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
It supports VMX
egrep '(vmx|svm)' /proc/cpuinfo
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good nopl aperfmperf pni dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm lahf_lm dtherm tpr_shadow vnmi flexpriority
And the virtualization options are enabled in BIOS.
I've set the ostype to both
Ubuntu_64 but neither work. I've also tried setting
VBoxManage modifyvm <vmname> --longmode on
"use a 32 bit image" isn't a solution, which is why I'm asking the question again. I see it's come up many times, and "your processor is 32 bit" is a very common response.
A potentially relevant piece of information is that the processor was upgraded after the initial installation of Ubuntu. I moved the processor that supports virtualization into this computer. I've had 64 bit VM's running on this machine before, with the same setup; I'm not sure if actually installing on the supported processor matters.